(a) Technical Field
The present disclosure relates to a Distance to Empty (DTE) calculation method for an electric vehicle. More particularly, it relates to a method by which a more accurate DTE calculation is provided by estimating the remaining available energy of the battery in the electric vehicle and using the estimated remaining available energy for calculating the DTE.
(b) Background Art
As is well known, electric vehicles are powered by motors driven via electricity charged in a battery.
In electric vehicles, it is very important to check a battery state such as the current temperature of the battery, the State of Charge (SOC) of the battery, etc., and to manage the battery state so as to maintain a predetermined level or higher. One of the reasons for checking and managing the battery state is to monitor the SOC of the battery in real time to inform a driver of a Distance to Empty (DTE) corresponding to the remaining capacity of the battery during driving.
In internal combustion engine vehicles, a driver is informed of a DTE estimated from the current fuel state. Similarly, in electric vehicles, a DTE (remaining driving distance) corresponding to the remaining capacity of the battery is estimated from the current battery energy state. This DTE may then is displayed on an instrument cluster (which typically contains gauges such as a speedometer, tachometer, odometer and fuel gauge, and indicators such as gearshift position, seat belt warning light, parking-brake-engagement warning light, and an engine-malfunction light) or the like.
A conventional DTE calculation method for an electric vehicle estimates a DTE by using a relationship between the SOC (%), which is the remaining energy in a high-voltage battery, and the energy consumption rate per distance.
FIG. 1 is a flowchart showing a conventional DTE calculation process. Referring to FIG. 1, the conventional DTE calculation process will be described.
The conventional DTE calculation method includes calculating a final fuel efficiency (S1) and calculating a DTE from the calculated final fuel efficiency (S2). More specifically, the conventional DTE calculation method includes calculating a past driving average fuel efficiency (km/%), calculating a current driving accumulative fuel efficiency (km/%), calculating a current driving section average fuel efficiency (km/%), calculating an official fuel efficiency (km/%) (or an authorized fuel efficiency, which is a value calculated and input in a fuel efficiency test mode corresponding to a vehicle model). Then, a final fuel efficiency is calculated by blending the past driving average fuel efficiency, the current driving accumulative fuel efficiency, the current driving section average fuel efficiency, and the official fuel efficiency. The DTE is then calculated from the calculated final fuel efficiency.
In this method, the past driving average fuel efficiency is calculated by averaging the fuel efficiencies of n past driving cycles (i.e., the interval from previous charging to next charging is defined as one driving cycle). The fuel efficiency (km/%) is calculated and stored at the end of every driving cycle (i.e., the previous driving cycle is finished when charging is initiated), and then the stored fuel efficiencies of the cycles are averaged.
In this case, the fuel efficiency (km/%) of the driving cycle is expressed as accumulative driving distance during a driving cycle (km)/ΔSOC(%), where ΔSOC(%)=SOC(%) immediately after previous charging−SOC(%) just before current charging.
The current driving accumulative fuel efficiency (km/%) is a fuel efficiency of the current driving cycle after charging.
The current driving section average fuel efficiency (km/%) is calculated by averaging the fuel efficiencies of n particular-sections of driving, in which the fuel efficiency is calculated and stored for every driving distance of a particular section and the stored fuel efficiencies are averaged.
When the final fuel efficiency is calculated, a DTE is calculated based on the final fuel efficiency and then displayed on the cluster or the like. In this case, a DTE (km) is calculated as ‘final fuel efficiency (km/%)×current SOC (%)’.
As such, in calculating a DTE of an electric vehicle according to the conventional method, the battery SOC is needed. More specifically, when the fuel efficiency of a past driving cycle is calculated, the total battery consumption (corresponding to the above ΔSOC) during cycles is reflected.
However, the conventional DTE calculation method calculates a DTE assuming that a battery SOC level is an available energy level. Thus, an error occurs in the DTE calculation because a value corresponding to a gas mileage (km/%) of an internal engine is used as a fuel efficiency (km/%).
In practice, since the battery SOC change and the battery available energy change are not the same, an error occurs in the DTE calculation as the correlation between the battery SOC change and the battery available energy change is reduced.
Therefore, additional compensation is required. However, the conventional DTE calculation method does not perform a correction with respect to the battery temperature and the battery electric current pattern (the vehicle driving pattern and the electric current pattern are the same as each other), resulting in further degradation of DTE calculation accuracy.
For example, when comparing driving at −10° C. with driving at 20° C., corresponding actual DTEs are different from each other.
Further, the battery SOC is a normalized value of an accumulative value of the amount of electric charge (an electric current value is calculated by integration). Thus, the battery SOC cannot accurately express the remaining available energy of the battery (the current battery available energy).
Moreover, a drop of the battery voltage occurs according to the electric current size and temperature of the battery, and a change in available energy occurs, such that accuracy is degraded in the DTE calculation based on the battery SOC (%).